A conventional type of aircraft wing or ‘high-lift section’ design is shown in FIGS. 1-4C and comprises a wing element 2 with a moveable ‘high-lift device’ in the form of a flap 3 attached to a trailing edge thereof. The flap 3 is moveable from a stowed position in which it is positioned in line with and in contact with the wing element 2 to form a single continuous wing/high lift section profile (see FIG. 4A). This configuration is used during cruise flight. The flap 3 can also be moved to a deployed position in which the flap 3 extends away from and downwardly relative to the wing element 2 (see FIG. 4B). This type of high lift section/wing design is known as a ‘slotted high lift system’ because in the deployed position, the flap 3 is spaced from the wing element 2 and thereby defines an aerodynamic slot 9 therebetween.
In use, when the flap 3 is in the stowed position, air flows over the upper and lower surfaces of the wing element 2 and flap 3 and merges at the trailing edge of the flap 3, as shown in FIG. 4A. However, when the flap 3 is in the deployed position, some of the air flow from the underside of the wing element 2 passes through the slot 9, over the leading edge of the of the flap 3, and along the upper surface of the flap 3, as shown in FIG. 4B. This increases circulation around the wing element 2 and the slot 9 is designed so that that pressure distribution around the flap 3, in particular, the peak pressure at the leading edge, is suppressed to prevent flow separation on the flap upper surface so that the air flow remains attached to the flap 3. When flow separation occurs at the flap 3, the high-lift section 1 experiences a significant loss in lift and so flow separation along the flap 3 is highly undesirable in such wing design.
The slot geometry formed by the two elements has a powerful influence on the flow quality over the high-lift elements. The dimensions used in measurement of slot geometry for any given flap deflection are shown in FIG. 3 and include ‘gap’ G—the shortest distance measured radially from the tip of the upper trailing edge of the wing element 2 to the flap surface; and ‘lap’ L—the distance from the front-most leading edge of the flap 3 to the upper trailing edge of the wing element 2 in the chordwise direction. As can be seen from FIGS. 4B and 4C, the flap 3 can be deployed at different angles, and it is important to ensure that the slot shape provides satisfactory aerodynamic performance for all possible flap deployment angles. Often, due to optimising the slot shape for a particular flap deflection, the resulting slot shape for other angles is not satisfactory and can result in high pressure gradients on the leading edge of the flap, resulting in flow separation. Such problematic slot shapes can include too large or too small slots, or where the slot is divergent or so-called ‘con-di’—i.e. initially convergent but then including a divergent portion towards the rear (see FIG. 3 for example). In addition, flow separation may occur with high flap deployment/deflection angles due to the pressure gradient on the flap becoming too large for the flow to remain attached along the length of the flap 3, even with the optimum slot shape (see FIG. 4C).
An alternative known type of wing/high-lift section configuration 20 is shown in FIGS. 5-8C. It comprises a wing element 22 but instead of a high lift device in the form of a flap being coupled to the trailing edge of the wing element, as in the embodiment shown in FIGS. 1-4C, it comprises a different type of moveable high-lift device in the form of a ‘slat’ 23 coupled to the leading edge of the wing element 22. Therefore, in this wing configuration, the ‘leading element’ is the slat 23 and the ‘trailing element’ is the wing element 22, whereas in the previous embodiment, the ‘leading element’ is the wing element 2 and the ‘trailing element’ is the flap 3.
In this alternative known wing configuration, the slat 23 is moveable to a deployed position (see FIG. 8B) where it is spaced from the wing element 22 to define an aerodynamic slot 29 therebetween. When the slat 23 is in the stowed position, air flows over the upper and lower surfaces of the slat 23 and wing element 22 and merges at the trailing edge of the wing element 22, as shown in FIG. 8A. However, when the slat 23 is in the deployed position, some of the air flow from the underside of the slat 23 passes through the slot 29, over the leading edge of the of the wing element 22, and along the upper surface of the wing element 22, as shown in FIG. 8B. This increases circulation around the slat 23, and the slot 29 is designed so that that pressure distribution around the wing element 22, in particular, the peak pressure at the leading edge, is suppressed to prevent flow separation on the wing upper surface so that the air flow remains attached to the wing element 22. When flow separation occurs at the wing 22 element, it results in a significant loss in lift and so flow separation along the wing element 22 is highly undesirable.
For both known wing/high-lift section configurations 1,20 described above, known measures exist in the prior art to reduce flow separation at the ‘trailing element’ upper surface (i.e. the upper surface of the flap 3 in the former wing embodiment 1, and the upper surface of the wing element 22 in the latter wing embodiment 20). One such measure is the addition of vortex generators attached to the leading edge of the trailing element which disturb the air flow and create vortices therein. This disturbed air flow in the form of downstream vortices suppresses separation of the air flow as it passes over the upper surface of the trailing element. However, this known prior art solution suffers from a number of drawbacks. Firstly, the discrete elements of the vortex generators must all be attached to a surface of the leading edge of the trailing element as a separate manufacturing step, increasing the cost and complexity of the manufacturing process. In addition, since the vortex generators are attached to the trailing element, they can become loose and fall off or can break off in operation of the aircraft and so require monitoring and replacement where necessary. Furthermore, since the vortex generators comprise elements upstanding from the trailing element upper surface, they take up space in the wing when the flap/slat is in the stowed position and so introduce space constraints in the wing design to accommodate them. Furthermore, since they project from the upper surface of the trailing element, they increase drag on the structure.
The present invention seeks to provide a wing for an aircraft that substantially alleviates or overcomes the problems mentioned above.